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    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
    <script>
        function reverse(arr){
            var newArr = [];
            for(i=arr.length-1; i>=0; i--){
                newArr[newArr.length] = arr[i]
            }
            return  newArr
        }
        var res = reverse([46,4,184,16,453,1])
        console.log(res);


        function fn(a,b){
            console.log(a,b);
        }
        fn(1)    // 1,   undefined
    </script>
</body>
</html>